This invention relates to an improved process for the provision of electric power during periods of peak demand therefor. Although electric power is utilized in diverse ways in the economy and demand remains high at all times, the demand for electric power nevertheless fluctuates markedly during the course of a day. Business demand is high throughout daylight hours in the operation of stores and offices but diminishes significantly thereafter. Residential demand is highest in the evening hours. Industrial demand is relatively steady and high at all times. Other demands, such as for urban transportation, peak at differing times. In an optimized power utilization system all such demands would be complementary and thus provide a substantially constant power requirement which could be served readily by the various sources of electric power in a readily predictable manner.
The uneven demand for electric power requires that power generation capacity be sufficiently great to accommodate the maximum instantaneous demand. This, in turn, leads to uneconomic operation of generally over-sized electric power generation facilities. One approach to this problem has been the encouragement of off-peak usage of electric power in an effort to re-structure the demand pattern. Another approach has been the installation of additional generating facilities intended for use during the periods of peak power demand.
An attractive installation of peak power generation facilities generally will be based on the prior storing of energy in a form readily convertible to electrical energy when the need therefor arises. For example, water may be pumped to elevated storage areas for subsequent generation of hydroelectric power. Similarly, air may be compressed and stored against its need in turbo-generation of electric power. Such storage of energy is effected by the consumption of power during off-peak demand periods so that the costs of such storage are substantial.
An attractive means for storing energy in the form of compressed air involves storage in underground reservoirs. Such reservoirs are available wherever a geological formation provides a caprock impermeable to gas, a rock dome therebelow, and artesian water filling the voids in an intermediate aquifer formation. Other suitable reservoirs exist in minedout areas, particularly areas where coal or salt has been removed. Introduction of a compressed gas, such as air, is accommodated by the displacement of the water which still provides a seal effective at the hydrostatic pressure prevailing in the particular formation. Such formations and their use in electric power generation are described, for example, in U.S. Pat. No. 3,523,192.
The cited patent describes a system for employing line power to compress air which is then piped to underground storage. Upon demand, compressed air is withdrawn from storage and sent through a turbine generator to generate needed line power. All operations are essentially adiabatic.
There exists a continuing need for more economic and technologically improved methods for providing electric power in response to the demand for such power during periods of maximum demand.